题解 | #统计农场牛数量#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    int sum = 0;

    int countNodes(TreeNode* root) {
        // write code here
        if(!root)
            return 0;

        sum += 1;
        countNodes(root->left);
        countNodes(root->right);

        return sum;
    }
};